Rapid dissolving polymer compositions and uses therefor

ABSTRACT

A particulate, free-flowing and rapid dissolving polymer composition is prepared by comminuting a high molecular weight thermoplastic or viscoelastic polymer at a temperature below its glass transition temperature while maintaining the polymer in an inert environment. A finely divided, solid coating agent is mingled with the comminuted polymer while maintaining the polymer particles in a cold and inert atmosphere. The particles of coating agent form a protective shell around each polymer particle by tumble mixing the components while raising the temperature of the mixture. The polymer composition finds use as a drag reducing agent; as an anti-misting agent; to enhance the efficiency of oil skimming processes and devices; and for the preparation of polymer solutions for other uses.

This is a division of application Ser. No. 807,947, filed Dec. 12, 1985,now U.S. Pat. No. 4,720,397.

This invention relates generally to the processing of high molecularweight polymers to form compositions which are readily dissolvable andto uses for these compositions.

More specifically, this invention relates to a method for producinghighly active, rapidly dissolving polymer compositions and to processesin which such polymer compositions find use.

High molecular weight, thermoplastic or viscoelastic polymers arenotoriously difficult to dissolve without degradation and withoutsignificant reduction in molecular weight. It is not uncommon for suchpolymers to require several weeks of gentle agitation in a solvent todissolve completely. Even then the concentration of polymer in suchsolutions is limited to a few percent at best because of the rapidincrease in viscosity with increasing polymer concentration.

Dilute solutions of high molecular weight polymers in solvents such ashydrocarbons display unusual and useful flow characteristics. Inparticular, certain linear polymers, such as the high molecular weightalpha-mono olefinic polymers are noted for their effectiveness as dragreducing agents and as anti-misting agents. A drag reducing agent is apolymer which, when dissolved in a solvent, substantially reduces thefriction loss during turbulent flow of the solution. An anti-mistingagent is a polymer which, when dissolved in fuel, serves tosignificantly increase median droplet size and reduce flammability offuel sprays caused by high velocity wind shear such as occurs during anaircraft crash landing.

A number of different approaches have been taken in the prior art to theproblem of preparing large quantities of extremely dilutesolutions-usually between five and about one hundred ppm--which arerequired for either drag reduction or anti-misting fuel use. Forexample, British Pat. No. 1,452,146 describes a method and apparatus fordissolving high molecular weight polymers on a large scale in solventssuch as crude oil without significant polymer degradation. Patentees usea dissolving vessel having at least two compartments formed by apartition with provision for liquid communication between thecompartments at the top and bottom of the partition. Polymer isintroduced into moving or agitated solvent within the vessel to form aslurry. Agitation is accomplished by sparging gas into the bottom of oneof the compartments to disperse the polymer particle throughout thesolvent so as to prevent the polymer particles from agglomerating and tospeed the dissolution process. Exemplary data set out in the patentshows the dissolving of crumb or cut polyisoprene of about 8 millionmolecular weight in crude oil at 32° C. to form a solution of about0.92% in about 120 to 160 hours. The molecular weight of the rubber wasreduced by about 10% during the dissolution. The maximum concentrationof polymer obtainable is determined by the viscosity of the finalsolution and, for high molecular weight polymers, maximum concentrationranges from about 0.5 to 2% by weight. The solution of polymer obtainedis then metered into a flowing stream of crude oil to provide dragreducing effects.

A very different approach to the dissolving of high molecular weightpolymers is shown by the Weitzen patent, U.S. Pat. No. 4,340,076.Weitzen found that high molecular weight polymers would very rapidly,almost instantaneously, dissolve in solvents for those polymers if thepolymer was comminuted at cryogenic temperatures and the resultingpolymer particles were introduced into the solvent without allowing themto warm. Polymer concentrations in the solution ranging from a few partsper million to 15% or more could readily be obtained. Essentially nopolymer degradation, as indicated by a reduction in the molecular weightof the polymer, occurs during the dissolution.

Yet another approach to the preparation of dilute solutions of highmolecular weight polymers is set out in the Mack patent, U.S. Pat. No.4,433,123. Here, a solution of a high molecular weight polymer, suitablefor use as a drag reducing agent or anti-misting agent, is produced bypolymerization of an alpha-olefin in a hydrocarbon solvent. The entiremixture, containing polyolefin, solvent and catalyst particles, is usedwithout separation to make up dilute solutions of the polymer in crudeoil or other hydrocarbons.

This last approach, to use the entire reaction mixture of apolymerization process, is presently most favored from a commercialstandpoint because of the great difficulties experienced in dissolvingsolid polymers without degradation. Drag reducing agents in field usetoday typically comprise a high molecular weight polymer dissolved inthe polymerization solvent, which may be hexane or heptane, at aconcentration ranging from a low of 2 to 3% to a maximum of 11 to 12%.These polymer solutions at typical commercial concentrations are thick,viscous liquids which are highly thixotropic and are also highlyviscoelastic. They are commonly transported and stored in containerswhich can be pressurized with an inert gas to pressures of 30 to 70 psigin order to discharge the liquid from the container. Generally speaking,the lower the polymer concentration, the more rapidly and easily it willdissolve in crude oil or other liquids. The upper limit to polymerconcentration is set by practical considerations including the need foran acceptably short dissolving time and the need to handle theconcentrated polymer solution using readily available and reasonablypriced equipment.

As may readily be appreciated, all three of the prior art approaches tothe preparation of polymer solutions for drag reducing or anti-mistingpurposes have significant disadvantages. Dissolving solid polymerdirectly into crude oil or other hydrocarbons is very time consuming,requires large dissolving vessels because of the long dissolving time,and almost inevitably results in significant degredation of the polymer.The Weitzen dissolving process requires a source of liquid nitrogen forits operation. The present commercial approach, which utilizes theentire polymerization mixture, is unwieldy because the polymer solutionmust be transported and stored in pressure vessels such as those used toship and store propane and butane. It also incurs a substantialfinancial penalty for transportation because little more than 10% of themixture is polymer; the active ingredient, in drag reducing orantimisting solutions. Also, the valuable solvent in which the polymeris dissolved cannot be recovered but instead becomes a part of the crudeoil stream.

It is evident that a more highly concentrated, but easily handleable andfast dissolving, form of polymer would offer significant advantages overpresent systems in drag reduction and anti-misting applications as wellas for a host of other uses.

SUMMARY OF THE INVENTION

Storage stable, non-agglomerating and rapid dissolving particulatepolymer compositions are prepared by chilling the polymer to atemperature below its glass transition temperature using an inertcryogenic refrigerant such as liquid nitrogen and comminuting thechilled and brittle polymer to form particles thereof. The polymerparticles are maintained at a temperature below the glass transitiontemperature of the polymer and are mixed with a finely divided, solidcoating agent. The coating agent must be a solid, must be non-reactivetoward the polymer and must have a median particle diameter less thanone-tenth the median diameter of the polymer particles. The coatingagent particles and the polymer particles are physically admixed whilewarming the mixture to and above the glass transition temperature of thepolymer resulting in the coating agent forming a multi-layered shellaround each polymer particle. The resulting polymer compositiontypically is free flowing and non-agglomerating. It may be used as adrag reducing agent or as an anti-misting agent by direct addition ofthe polymer composition into a crude oil or hydrocarbon fuel streamwherein the polymer rapidly dissolves without agglomeration.

Hence, it is an object of this invention to prepare polymer compositionsin a form which is convenient for transport, storage and solutionmaking.

It is another object of this invention to provide particulate polymercompositions wherein each polymer particle has an encompassing,multi-layered shell of a solid coating agent.

Yet another object of this invention is to provide a simple andconvenient process for reducing the flowing friction of hydrocarbons ina pipeline.

It is another object of this invention to provide a method for thepreparation of dilute polymer solutions.

Other objects of this invention will be apparent from the followingdescription of preferred embodiments and exemplary uses.

BRIEF DESCRIPTION OF THE DRAWING

Certain exemplary embodiments of the invention are illustrated in thedrawing in which:

FIG. 1 is a stylized view of a partial cross section of a single coatedpolymer particle;

FIG. 2 is a photo-micrograph of a single, coated polymer particle;

FIG. 3 is a photo-micrograph at higher magnification showing details ofthe coating surface; and

FIG. 4 is a diagrammatic flowsheet of a process for reducing the flowingfriction of hydrocarbons in a pipeline.

DESCRIPTION AND DISCUSSION OF THE INVENTION

Various embodiments of this invention will be described and discussed indetail with reference to the drawing figures in which like referencenumerals refer to the same component illustrated in different figures.

Referring first to FIG. 1, there is shown a portion of a single particle10 of a polymer composition prepared in accordance with this invention.The composition comprises a center, or core, polymer particle 11 shownhere in section. Polymer core particle 11 is preferably prepared bycomminuting a more massive form of the polymer, in granulated or crumbform for example, using a hammer mill, pin mill or other suitablecomminuting means. The polymers used in preferred embodiments of thisinvention comprise those thermoplastics, both natural and synthetic,which impart viscoelastic properties to a solution. Such polymerstypically display glass transition temperatures in the range of about-10° C. to about -100° C. At temperatures below the glass transitiontemperature, the polymers become brittle and can be readily comminutedby use of impact-type mills. Exemplary polymers useful in this inventioninclude polyisobutylene, polyisoprene, polyalphaolefins, polybutadiene,copolymers of styrene and butadiene, copolymers of ethylene andbutene-1, fluoroelastomers such as the copolymers of vinylidene fluorideand hexafluoropropylene and other polymers of a generally similarnature.

In order to successfully comminute the polymers useful in thisinvention, it is necessary to chill the polymers below their glasstransition temperature and to maintain the temperature below that pointduring comminution. Chilling is most conveniently accomplished by use ofa liquid cryogenic refrigerant, preferably liquid nitrogen. Comminutionof the polymer produces fragments or particles having fresh, cleansurfaces. It has been found that preservation of these clean surfaces ismandatory if rapid dissolution of the polymer particles in a solvent isto be obtained. It is believed that active sites on freshly cleavedpolymer surfaces react with the oxygen and water vapor normally presentin the atmosphere to produce a film or skin around the particle whichinhibits or greatly slows the dissolution of the polymer in a solvent.For this reason, it is mandatory also that the comminution be carriedout in an inert atmosphere. The twin requirements of chilling thepolymer and maintaining it in an inert atmosphere during comminution arebest met through use of liquid nitrogen as a cryogenic refrigerant andinerting agent. It is possible, but not economically practical, to useother inert cryogenic refrigerants such as liquid argon rather thanliquid nitrogen.

Polymer particles resulting from comminution are commingled with aparticulate coating agent 12 while continuing to maintain the polymerparticles in a chilled and inert atmosphere. The coating agent 12 mustbe a solid at ambient to moderately elevated temperature; must benon-reactive toward the polymer; and, most importantly, must have aparticle size that is much smaller than is the particle size of thepolymer. It is necessary that the median diameter of the coating agentparticles 12 be less than one-tenth the median diameter of the polymerparticles 11 and it is preferred that the difference in particle sizebetween the two substances, coating agent and polymer, be substantiallygreater than that.

The particle size to which the polymer is comminuted is not critical butpolymer particle size does affect the dissolving rate of the polymercomposition in a solvent. It is generally preferred that the medianpolymer particle diameter be less than about 0.5 mm, or about 35 mesh.Additional advantage is often gained by reducing the median polymerparticle diameter below about 0.075 mm which is equivalent to about 200mesh. In all cases it is preferred that the median diameter of coatingagent particles be less than about 0.01 mm or 10 micrometers. Experienceto date indicates that the best results are obtained with coating agentshaving a median particle diameter of about 0.1 to about 10 micrometers.

The commingled polymer particles 11 and coating agent particles 12, inan inert atmosphere and at a temperature below the glass transitiontemperature, are then continuously mixed as by tumbling while themixture is warmed to and above the glass transition temperature of thepolymer. This procedure may conveniently be accomplished in a batch-wisefashion using a rotating V-Type blender. Heat transfer from theatmosphere through the blender shell is sufficient to warm the chilledmixture to and above the glass transition temperature of the polymer. Itis preferred that tumble mixing be continued until the mixtureapproaches ambient temperature.

Tumble mixing of the polymer particles and coating agent while allowingthe temperature to warm results in the formation of composite particles,each having a central core consisting of a solid polymer particle 11with a multi-layered shell 13 surrounding the core and made up ofparticles 12 of the coating agent. It is, of course, necessary toprovide a sufficient amount of coating agent relative to the polymerparticles to allow for the formation of that multi-layered shell. Theminimum amount of coating agent required on a weight or percentage basisdepends upon the relative size of the coating agent particles ascompared to the polymer particles as well as upon the specific gravityof the components and will generally be in excess of 15% by weight ofthe mixture. The optimum amount of coating agent usually is considerablyhigher than that and typically ranges from about 20% to about 75% byweight of the composition.

The multi-layered shell 13 of coating agent particles tightly adheres tothe polymer core particle 11 and is not disrupted by physical handling.There are a number of reasons for the stability and physical integrityof the coating agent shell. Those polymers useful in this inventiongenerally display a surface tackiness at temperatures above the glasstransition temperature. Consequently, polymer particles, especiallythose particles having freshly formed surfaces, tend to agglomerate orstick together. At temperatures below the glass transition temperature,however, those same polymers form free flowing and non-adherentparticles. Tumble mixing of the polymer particles with the much smallercoating agent particles while the temperature is raised through theglass transition temperature allows the polymer particles to be coatedprior to the formation of tacky polymer surfaces.

There are other considerations of equal or possibly greater importance.The interaction between very finely divided particles to formagglomerates is well known. Also, the adherence of microscopic particlesto solid surfaces is well known and has been much studied. For example,particles having a diameter of less than about 10 micrometers adhere sostrongly to surfaces that accelerations of the order of 10³ to 10⁴g-units are not sufficient to dislodge them from the surface. The forcesinvolved in the adhesive interaction of small particles, one to anotheror to the surface of a larger particle, include molecular forces and tosome degree Coulomb forces; the magnitude of these forces decreasingrapidly with increasing distance between the contiguous surfaces. Otherforces arise when two particles contact each other or the surface of alarger particle. Such forces include electrical interactions due tosurface charges and the like.

The surfaces of all of the particles, coating agent particles andpolymer particles alike, also adsorb a gas layer. The gas adsorbed isthat inert gas which is present during the formation of the compositeparticles through mixing and warming; usually nitrogen. All of theinterstices 14 between and around coating particles 12 making up themultilayered shell 13 also are filled with nitrogen or other inert gas.Consequently, the composite particles 10 may be exposed to theatmosphere and freely handled without use of cautionary measures becausethe surfaces of each polymer particle 11 are protected from atmosphericcontact by inert gas adsorbed on and filling the interstices betweencoating agent particles 12.

Structural details of the composite particles 10 and particularly of theexterior surface of shell 13 are shown in FIGS. 2 and 3 which areelectron micrographs of composite particles prepared by the process ofthis invention. In both of FIGS. 2 and 3, the particle core is a highmolecular weight polyisobutylene while the coating agent is very finelydivided tricalcium phosphate (TCP). FIG. 2 shows a single particle 10having a diameter of about 0.1 mm (100 micrometers) as is shown by thescale across the bottom of the Figure. This Figure clearly shows theclose packed nature of the TCP particles making up the exterior shell ofparticle 10. FIG. 3 is a detailed view of the surface of a particle 10at much higher magnification. As can be seen by reference to the scaleat the bottom of this Figure, the individual particles are typicallymuch less than one micrometer in diameter. It may also be appreciatedfrom study of this Figure how effectively shielded from atmosphericcontamination is the central polymer core by the multi-layered TCPcoating with the nitrogen gas adsorbed on particle surfaces and fillingthe interstices between particles.

As has been set out previously, the coating agent must be a solid atambient to moderately elevated temperature; must be non-reactive towardthe polymer; and must have a particle size that is much smaller than isthe particle size of the comminuted polymer particles. In experimentaltests using a variety of coating agent compositions, it was found thatall compositions tested were operative to produce coated polymerparticles in accordance with this invention provided that the criteriaset out above were met. Coating agents tested included amorphous silicondioxide, kaolin clay, calcined kaolin clay, graphite, Teflon powder andtricalcium phosphate.

This is not to say, however, that the compositions obtained through useof the different coating agents are all of the same or equal usefulness.The properties of the coating agent used, its wettability byhydrocarbons for example, do affect the results obtained in specificprocess applications. One such process application is the use of thepolymer compositions of this invention as drag reducing agents in theflow of hydrocarbons, especially crude oil, through pipelines. Polymercompositions having a tricalcium phosphate (TCP) coating are presentlypreferred for these uses.

FIG. 4 illustrates the simplicity of approach and apparatus required forpipeline drag reduction allowed through use of the compositions of thisinvention. There is shown a segment of a pipeline 21 having crude oil,or other hydrocarbon stream, flowing in the direction of the arrow 22.The crude oil in pipeline 21 typically would be at a pressure in therange of about 500 to 1,500 psig and would be flowing at a rate of about4 to 15 feet per second. A side-stream 23 is removed from the pipelineand is let down to near atmospheric pressure through pressure reducingmeans 24. The low pressure oil stream 25 is directed to a liquid-solidsmixing means 26 which feeds into the inlet of pump 27. Particles 10 ofthe polymer composition of this invention are also introduced intomixing means 26 which may comprise a conical, open-topped vessel havinga bottom opening communicating directly with the inlet of pump 27. Pump27 must be capable of discharging a metered stream 28 of the oil andpolymer composition slurry from mixing vessel 26 into the high pressurepipeline 21. It has been found that a rotary, positive displacement gearpump is appropriate for use in this application.

The mixing means 26 and pump 27 must be so arranged that the hold-uptime of the polymer composition-hydrocarbon slurry, as it passes frommixing means 26 to the interior of pipeline 21, is limited to a fewseconds. A relatively short hold-up time is necessary because of therapidity with which polymer composition 10 dissolves in hydrocarbons. Asubstantial degree of dissolution occurs within 20 to 30 seconds ofcontact by the polymer composition 10 with a hydrocarbon. Were anysubstantial degreee of dissolution to be allowed before entry of theslurry into pump 26, the viscosity of the mixture would increase andcause difficulties in pumping.

The polymer composition presently preferred for drag reduction usecomprises a high molecular weight polyisobutylene core having a shellcoating of tricalcium phosphate (TCP) prepared using liquid nitrogen asthe refrigerant and inerting agent. Typical compositions comprise about50% by weight each of polymer and of TCP coating. The composition is afree flowing powder which is stable in storage and which can be exposedto the atmosphere for many hours without loss of dissolving activity.

In contrast, commercial drag reducing agents are prepared as extremelyviscous solutions containing a maximum of about 10% to 12% polymer byweight. The solutions must be shipped and stored in containers which canbe pressurized to 50 psig or more with an inert gas in order to forcethe viscous liquid from the container. In at least some instances thedrag reducing agent does not dissolve quickly enough in crude oil so alighter solvent, which may be a distilled fraction from the crude oil,is provided to enhance the dissolving rate. As may be appreciated, astable, powdered polymer composition having a polymer content of about50% by weight and directly injectable into a pipeline providessubstantial practical and economic advantages over those drag reducingagents provided in dissolved form as is now the standard in the art.

The amount of polymer required to provide a significant drag reducingeffect depends to a great degree upon the molecular weight of thepolymer and to a lesser degree upon the characteristics of the crudeoil. Generally speaking, the effectiveness of a polymer as a dragreducing agent increases as an exponential function of its molecularweight. With those polymers in use today, polymer concentrations incrude oil range from about 2 to about 100 ppm, and most usually fromabout 5 to 50 ppm, to obtain the optimum drag reducing effect.

Certain polymer compositions of this invention may be slurried in waterwithout affecting the stability of the exterior shell and withoutaffecting its later wettability by hydrocarbons. For example, polymercompositions having an external particulate shell of TCP can be slurriedin water and thereafter introduced into a hydrocarbon whereupon thepolymer particles are immediately wet by hydrocarbons which penetratethe TCP shell with rapid dissolution of the polymer in the hydrocarbons.This characteristic of TCP-coated polymer compositions allows amodification of the process of FIG. 4. It is possible, and sometimesdesirable, to dispense with oil side-stream 23 and provide instead awater stream (equivalent to oil stream 25) to the liquid-solids mixingmeans 26. The small quantity of water introduced into pipeline 21 as aslurrying liquid for the polymer composition is generally of nopractical consequence as most crude oils normally contain at least smallconcentrations of water. The amount of liquid, whether oil or water,necessary to produce a pumpable slurry of the polymer composition issmall; typically ranging from about 1 to 5 parts of liquid per part ofpolymer composition.

The process depicted in FIG. 4 may also be employed for the productionof anti-misting fuels suitable for use in turbine and diesel engines. Inthis instance, line 21 would comprise an aircraft or land vehiclerefueling line and polymer composition 10 would comprise a very highmolecular weight polymer. Shell 13 would preferably consist of veryfinely divided (preferably less than 1 micrometer in diameter) TCP orgraphite particles. Polyisobutylene of a molecular weight greater than 5million is the most preferred polymer for this use.

It is well known in the art that polymeric solutes in jet or dieselfuels can serve to greatly increase the droplet size and reduce theflammability of fuel sprays created by high-velocity wind shear. It isalso recognized that the effectiveness of the polymers used increaseswith molecular weight. It order to obtain effective anti-mistingactivity, it is necessary to add to the fuel sufficient polymer tosubstantially eliminate that population of fuel droplets having adiameter of less than about 50 micrometers normally produced when purefuel is subjected to wind shear. While the amount of polymer required toachieve this result depends substantially upon the polymer molecularweight, concentrations of polymer in the fuel ranging from about 5 toabout 100 ppm by weight are generally appropriate. The coating agent,TCP or graphite, is either retained on the fuel filters normallyemployed in aircraft or land vehicle fuel systems or harmlessly passesthrough the filters and engines.

Yet another significant area of use for the polymer compositions of thisinvention is in the mechanical recovery of spilled hydrocarbons from awater surface. It is common practice today to remove spilledhydrocarbons from the surface of water using a variety of mechanicalskimmers including those which use weirs, vacuum nozzles, disks, a drumor a belt to contact the oil and remove it from the water surface.Performance of the various types of skimmers is closely related to theproperties of the oil, particularly the viscosity of the oil. Each ofthese skimmers has the ability to rapidly clean the oil from the areaimmediately around it. After that time, the performance of a skimmer isdetermined not by its own capability to pick up oil but by the rate atwhich new oil flows across the water surface to the skimmer and by therate at which the skimmer can be moved to new patches of oil.

All of the skimmers, whether they be a vacuum apparatus, a weir, a disk,drum or belt type, are limited in the rate at which they can beoperated. For example, with a disk skimmer, the more rapidly the disksare rotated the greater the rate of oil pick-up until a maximum value isreached. Above a certain rotational speed, oil tends to be flung off thedisk. Also, the rate of replenishment of oil on the water surfaceadjacent the disk limits the rate of oil pick-up. As can be appreciated,the viscosity of the spilled oil plays a major role in defining themaximum pick-up rate as viscosity affects both the oil loading on thedisk (or other moving surface) as well as the flow rate of oil acrossthe water surface.

It has been found that spreading the polymer composition of thisinvention in low concentration across the surface of a spilled oil orother hydrocarbon imparts viscoelastic properties to the oil as thepolymer dissolves therein. The viscoelasticity imparted to the oilimproves in dramatic fashion the performance of conventional oilskimmers. As the oil layer is pulled from the water surface by theskimmer, the viscoelasticity imparted to the oil by the dissolvedpolymer causes the oil layer to act as a stretchable rubber-like sheet.A disk or drum skimmer can then be operated at a higher rotationalvelocity without oil being flung from the disk or drum surface. Becauseof the viscoelasticity, oil is replenished at the skimmer site much morerapidly than is the case with untreated oil. Further, the oil as it isbeing depleted from the water surface does not break up into patches butrather is pulled in to the skimmer. All of these effects combine toenhance the recovery efficiency of a conventional skimmer by a factor asgreat as 3 to 6.

The concentration of polymer required to produce an adequate degree ofviscoelasticity in a spilled oil depends in large part upon themolecular weight of the polymer and upon the viscosity of the oil.Generally speaking, the higher the polymer molecular weight and thehigher the oil viscosity, the lower is the polymer concentrationrequired to provide sufficient viscoelasticity to substantially improveskimmer performance. About 50 ppm by weight of polymer in crude oilrepresents about the lowest practical concentration to obtainsignificant improvement in skimmer efficiency. Little improvement isgained by providing polymer concentrations in excess of 1.0%, or 10,000ppm, and in most instances appropriate concentrations of polymer in theoil will range from about 100 to 1000 ppm.

The polymer composition may be distributed across the surface of an oilspill using any conventional device ordinarily used for the spreading ofparticulate solids such as seeders, fertilizer spreaders, blowers andthe like. A polymer composition comprising a very high molecular weight(above 5 million,) polyisobutylene having a multi-layered shell of TCPparticles is particularly preferred for this application as the TCPshell is not affected by contact with water.

Various embodiments of the invention are more specifically describedwith reference to the following examples which are provided to furtherillustrate but not to limit the invention.

EXAMPLE 1

A quantity of high molecular weight polyisobutylene, designated asOppanol B246 by the supplier, BASF, was obtained. The polymer was in theform of generally cubic chunks about 1 cm on a side and had been mixedwith about 10% by weight of powdered tricalcium phosphate to keep thepolymer chunks from sticking together.

The polyisobutylene chunks were fed, together with sufficient additionaltricalcium phosphate (TCP) to form a 50-50 by weight mixture of the twocomponents, into a cryo-chiller cooled with liquid nitrogen. Thecryo-chiller discharged into a hammermill, which was cooled withadditional liquid nitrogen and equipped with an 0.062 inch, round-holedscreen. The comminuted mixture of polyisobutylene and TCP was collectedcold and maintained under a protective atmosphere of nitrogen. Thismixture was then re-ground using the same hammermill but equipped with a0.013 inch herringbone screen. Again the reground mixture was collectedcold and maintained under nitrogen.

The TCP used was obtained from the Stauffer Chemical Company, wasanhydrous having the chemical formula 3Ca₃ (PO₄)₂. Ca(OH)₂, had a bulkdensity of approximately 20 lb/ft₃, and had a median particle size ofless than about 1 micrometer as observed by electron microscopy.

A sample of the ground mixture, which was at a temperature approximatingthe boiling point of liquid nitrogen, was removed and examined visuallyunder a microscope. The relatively large polyisobutylene particles wereirregular and angular in apperance having sharp edges and vertices.Particles of TCP flowed freely around and among the polymer particles.This sample was allowed to warm to room temperature over a two-hourperiod and was again examined visually. The polyisobutylene particleshad become much more rounded and softened in shape with a disapperanceof the sharp edges and angulartly previously observed.

The bulk of the ground mixture, weighting about 300 kg and comprisingabout equal weight fractions of TCP and polyisobutylene, was thentransferred while cold and under a nitrogen atmosphere into a large,uninsulated, V-blender. The blender was rotated for about 20 minuteswhile the contents warmed by means of heat transfer through the blendershell. At the end of that time, the blender contents had warmed to nearambient and were free flowing, homogeneous and granular in apperance. Nofree polymer or TCP particles could be seen by visual inspection. Theblender contents were then packaged in plastic bags.

Samples of the composition were examined by electron microscopy. FIGS. 2and 3 are exemplary photomicrographs obtained.

EXAMPLE 2

A small quantity of the composition of Example 1 was added to a beakercontaining diesel fuel. Particles of the composition were readily wet bythe diesel fuel. The polymer core of the particles dissolved so rapidlythat viscoelastic properties were imparted to the liquid within about 20seconds as evidenced by the formation of strands when a stirring rod wasremoved from the liquid.

Other particles of the composition were placed on a microscope slide andarranged for viewing. Several drops of isooctane were placed on one endof the slide. As the isooctane contacted particles of the composition,the particles were seen to swell rapidly with the granular TCP coatingcracking and falling apart as the polymer dissolved in the isooctane.

Particles of the composition were placed on another microscope slide andarranged for viewing. Several drops of water were placed on one end ofthe slide in the same manner as was the isooctane. So far as could bevisually observed, water had no effect on the particles of thecomposition.

EXAMPLE 3

A sample of polyisobutylene particles coated with TCP prepared in themanner of Example 1 and weighing 1.5 g was placed in 250 ml of water ina stirred beaker. After a period of agitation, the slurry was allowed tosettle for about one-half hour at which time essentially all of theparticulate composition had settled to the bottom leaving a relativelyclear supernatant liquid. The supernatant was decanted off and a fresh250 ml portion of water was added. This stirring, settling anddecantantation procedure was repeated for a total of four times on thesame sample in order to determine the stability of the TCP coatingtoward water.

The settled slurry was filtered through qualitative filter paper and thefilter cake was allowed to air dry for about 30 minutes. It was thenvisually inspected using a stereo microscope. The particles were freeflowing and non-agglomerating and all of the particles appeared to havean intact coating of TCP. As was noted previously, the particles settledin water indicating a specific gravity greater than 1.0. Polyisobutylenehas a specific gravity less than 1.0 and the TCP used in making thecomposition had a bulk density of about 201b/ft³ ; about one-third thedensity of water. This particular lot of TCP-coated polyisobutylenecontained about 52% polyisobutylene and 48% TCP by weight. It is evidentfrom these considerations that the shell of TCP particles surroundingeach core particle of polyisobutylene is very closely and tightlypacked.

The dissolving rate in cyclohexane of particles of the filter cake wasvisually compared on a microscope slide with the dissolving rate ofunwet particles of the same composition. No differences in dissolvingrate were observed. It was concluded that extensive water contact withthe TCP coating does not adversely affect the rate at which thecomposition particles will dissolve in an organic liquid.

EXAMPLE 4

A small quantity of polyisobutylene particles coated with TCP preparedin the manner of Example 1 was placed on a microscope slide and arrangedfor viewing. A 10% solution of nitric acid was added in a drop-wisefashion at one end of the slide. The advancing liquid acid completelydissolved the TCP coating around the particles leaving clean, glass-likecore particles of polyisobutylene. A needle probe was used to bring thecleaned, core particles into contact with one another. As soon as onecore particle touched another, the two adhered, or fused, togetherforming an agglomerate which could not be separated by manipulation ofthe agglomerate with probes.

In a generally similar experiment, the TCP-coated, polyisobutyleneparticles were suspended in a quantity of stirred water. Again, nitricacid was added in a drop-wise fashion until the TCP coating was entirelydissolved. At this point, the suspension cleared and several ball-likemasses of polyisobutylene formed from the agglomerated core particles.By weighing the sample of polymer composition and by measuring theamount of acid of known concentration required to dissolve the TCPcoating, this procedure may be used to determine the ratio of TCP topolyisobutylene making up the composition.

EXAMPLE 5

A procedure generally similar to that of Example 1 was employed toprepare a composition consisting of polyisobutylene and kaolin clay. Thepolyisobutylene and clay were co-ground in a liquid nitrogen-cooledhammer mill having an 0.062" herringbone screen. The comminuted mixturewas collected cold and was re-ground in the same liquid nitrogen-cooledhammer mill now equipped with an 0.013" herringbone screen. The mixturewas then placed in a laboratory V-blender which had been pre-chilledwith liquid nitrogen and was tumble mixed for 30 minutes while allowingthe mixture to warm.

The resulting particulate composition was generally similar to thatobtained when using TCP as a coating agent. Liquid hydrocarbons such asisooctane and diesel fuel readily wet and penetrated the clay shell withsubsequent rapid dissolution of the core polymer particle. Unlike TCPcoatings, however, the clay was readily removed upon agitation of thecomposition in water resulting in agglomeration of the core particles.

EXAMPLE 6

A procedure generally similar to that of Example 5 was employed toprepare a composition consisting of polyisobutylene and a precipitated,amorphous hydrated silicon dioxide sold under the tradename Zeosyl 200.According to the manufacturer's specification sheet, this material hasan average particle size of 4-6 micrometers as determined by the CoulterCounter Method. The resulting composition was similar in properties tothat of Example 5.

EXAMPLE 7

A procedure generally similar to that of Example 5 was employed toprepare a composition consisting of polyisobutylene and graphite powder.The graphite powder was a product of Asbury Graphite Mills and was soldunder the tradename Micro No. 270 .

The polyisobutylene, BASF B-200, was first granulated cold through a 0.5inch screen and collected in liquid nitrogen. It was again granulated,this time through a 3/32 inch screen, and again collected in liquidnitrogen. The granulated polymer was then mixed with graphite powder ina ratio of approximately 2:1 by weight. This mixture was ground in ahammer mill fitted with an 0.020 inch screen and the mill output wascollected in a liquid nitrogen-chilled vessel provided with a securelyclosing top having pressure venting means. The mixture within the vesselwas tumble mixed while it warmed and was then allowed to standovernight.

A sample of the resulting composition was added to a quantity ofkerosene in an amount sufficient to provide a 250 ppm concentration ofpolymer in the kerosene. The dissolving rate was very fast as evidencedby the fact that a significant degree of viscoelasticity had developedin the solution within 20 seconds of addition. The dissolvingcomposition gave a black, smoky looking, birefringent solution.Filtration of the solution through a qualitative grade filter paperresulted in the removal of the graphite leaving a clear solution.

EXAMPLE 8

A composition consisting of an experimental anti-misting polymerdeveloped by the Shell Oil Company and designated SAP-960 together withan equal weight of TCP was prepared by first grinding the two materialstogether in a liquid nitrogen-cooled hammer mill equipped with an 0.062inch herringbone screen. The ground mixture was collected at liquidnitrogen temperatures and was re-ground through a 0.027 inch screen. Itwas then tumble mixed in a V-blender for 30 minutes while allowing themixture to warm up.

The resulting composition was indistinguishable in appearance from thatobtained in Example 1. It reacted in the same manner to the testsdescribed in Examples 2-4 as did the TCP-coated polyisobutyleneparticles.

EXAMPLE 9

A composition comprising core particles of Viton A and having anencompassing shell of Teflon particles was prepared. Viton A is afluoroelastomer being a copolymer of vinylidene fluoride andhexafluoropropylene. The Teflon particles were designated Teflon 7-C bythe manufacturer, DuPont, and are generally used in extrusion andsintering fabrication procedures.

The Viton A was comminuted by chilling it with liquid nitrogen andpassing it through a hammer mill. It was then mixed with Teflon 7-Cpowder in a weight ratio of Viton A to Teflon of approximately 1:2 andthe mixture was re-ground to reduce the size of the Viton A and toobtain mixing of the two materials. Both the first and second grindingprocedures were carried out with liquid nitrogen cooling.

The comminuted material was then tumble mixed while warming to obtain arelatively free flowing, homogeneous particulate composition. Thiscomposition could be readily mixed with other solids and could beextruded at moderate pressures and temperatures.

EXAMPLE 10

The composition of Example 1 was employed in a series of drag reductiontests in which the composition was introduced into a pipeline using theprocedure illustrated by FIG. 4. The composition was introduced into thecrude oil flowing within the pipeline at rates which provided apolyisobutylene concentration in the crude oil ranging from about 5 ppmto about 20 ppm. A substantial increase in the flow rate of the crudeoil was observed as a result of the polymer addition.

EXAMPLE 11

The composition of Example 1 was dissolved in kerosene to obtainsolutions having a polyisobutylene concentration ranging from about 1 to10 ppm. The resulting solutions were passed through a fine nozzle andthe exiting fluid streams were photographed at very high speeds andresolution. Kerosene without dissolved polymer produced a largepopulation of very tiny droplets. As the polymer concentration in thekerosene increased, the population of tiny droplets in the nozzle streamdecreased rapidly and, at the higher polymer concentrations, essentiallydisappeared.

EXAMPLE 12

A number of the polymer compositions described in the foregoing exampleswere tested to determine their efficiency in oil spill clean upprocesses. A laboratory model disk skimmer was constructed and consistedof a single disk with its axis oriented horizontally at a level abovethe surface of water within a test container. Means were provided at anupper portion of the disk to wipe and remove collected oil from thedisk. The rotational speed of the disk was controllable over a widerange.

Tests were run using diesel fuel and a medium weight oil as the spilledhydrocarbons. In each case, a base performance level of the skimmerusing the neat hydrocarbon was determined over the range of usable diskrotational speeds. Thereafter, a series of tests were run on eachhydrocarbon at different polymer concentrations and skimmer speeds. Itwas found that the addition of sufficient quantities of the polymercompositions of this invention to impart viscoelastic properties to thespilled hydrocarbon in all cases significantly enhanced skimmerperformance. A recovery enhancement factor was arbitrarily defined to bethat ratio of the time required to pick up a unit volume of neathydrocarbon divided by the time required to pick up a unit volume ofhydrocarbon treated with the polymer compositions of this invention.Recovery enhancement factors of 2 to 3 were routinely achieved.

It was observed that substantial viscoelasticity was imparted to themedium weight oil at dissolved polymer concentrations as low as 50 to100 ppm. In addition to increasing the hydrocarbon loading on the disk,the viscoelasticity tended to prevent depletion of the oil on the watersurface adjacent the disk. Oil was continually drawn to the rotatingdisk from distant areas of the water surface. Further, the oil did notbreak up into patches or clumps as is commonplace with the untreated, orneat, oil.

Confirmatory tests were performed using several different types offull-size, commercial skimmers on a test pond. The performance of theskimmers operating on spilled hydrocarbons having a sufficient amount ofthe polymer composition of this invention dissolved therein to renderthe spilled hydrocarbons viscoelastic exceeded the expectations gainedfrom laboratory experimentation.

The above examples have been set out to illustrate a number of specificembodiments of this invention. The data and observations presentedtherein are not to be construed as limiting the scope of the inventivecompositions nor their uses.

We claim:
 1. A rapid dissolving, particulate, polymer compositioncomprising:a central core consisting of a solid polymer particle havingclean surfaces; a multi-layered particulate coating agent entirelysurrounding said core, the median diameter of the particles of saidcoating agent being less than one-tenth the diameter of said polymercore; and a gas filling the interstices between said coating agentparticles and around said core, said gas being non-reactive toward saidclean core surfaces.
 2. The composition of claim 1 wherein said polymercomprises a natural or synthetic thermoplastic which impartsviscoelastic properties to a solution of said polymer in a solvent andwherein said clean polymer surfaces comprise fracture surfaces createdby comminution in an inert atmosphere at a temperature below the glasstransition temperature of said polymer.
 3. The composition of claim 2wherein said gas filling the interstices between coating agent particlesis nitrogen.
 4. The composition of claim 3 wherein said polymer isselected from the group consisiting of polyisobutylene, polyisoprene,polyalpha-olefins, polybutadiene, copolymers of styrene and butadiene,copolymers of ethylene and butene-1, copolymers of vinylidene fluorideand hexafluoropropylene and mixtures thereof.
 5. The composition ofclaim 3 wherein said coating agent is selected from the group consistingof amorphous silicon dioxide, kaolin clay, calcined kaolin clay,graphite, Teflon powder and tricalcium phosphate.
 6. The composition ofclaim 3 wherein the median diameter of said central core is less thanabout 0.075 .
 7. The composition of claim 3 wherein the median particlediameter of said coating agent ranges from about 0.1 to about 10micrometers.
 8. The composition of claim 3 wherein said coating agentparticles make up from about 20% to about 75% by weight of thecomposition.
 9. The composition of claim 3 wherein said polymer ispolyisobutylene and wherein said coating agent is selected from thegroup consisting of tricalcium phosphate, kaolin clay and graphite. 10.The composition of claim 9 wherein said coating agent is tricalciumphosphate.
 11. The composition of claim 3 wherein said polymer is afluorinated elastomer and wherein said coating agent is Teflon powder.